Genistein and daidzein are estrogenic isoflavones found in soybeans. Although they are about 1/10,000 as potent as estradiol, infants fed soy formula have serum concentrations that are up to 4 orders of magnitude higher than estradiol. Clinical trial data show increases in cholesterol synthesis consistent with an estrogen effect in infants fed soy formula vs. human milk or cow milk formula, and lowered response to polio vaccination, which might or might not be an estrogen effect. Anatomic, sonographic, and other biochemical evidence of estrogen exposure has not been looked for in infants fed soy. Whether such widely used products do or do not have clinically detectable estrogenic activity in infants, the group with the highest exposure per kilo, is important clinically; in addition, it may be a crucial test of the ability of laboratory measures of estrogenicity to predict actual endocrine response in humans. We have begun pilot studies to examine the natural history of estrogen responsive physiology in the newborn, and will use the results to develop a longitudinal study of the possible estrogenic effects of soy formula on infants. At the Boston Children?s Hospital, our collaborators in pediatric ultrasound have developed and assessed inter- and intra- rater reliability for examinations of the breast, uterus, ovaries, testes, prostate, adrenals, and thyroid. Using a protocol and eligibility criteria developed at NIEHS, by fall 2004 they will have examined 96 girls, ranging in age from less than 48 hours to one year, and 60 boys, ranging in age from less than 48 hours to 6 months. We find that the methods are reliable, ans that uterine and ovarian volume changes over time but that the endometrial stripe does not. Breast tissue and accompanying fat is readily imaged. At the Children?s Hospital in Philadelphia, our collaborators are doing physical examinations of the breasts and genitalia of 84 children total of both sexes ages from less than 48 hours to 6 months. This examination is a modification of the well-known Ballard scale for gestational age, which uses the degree of estrogen response by the breasts and genitals. The degree of estrogenization is so strongly related to gestational age that the weeks in utero for the child can be estimated using this examination. We find that breast tissue varies over time, and that fat is distinguishable from gland. We also find that vaginal wall cells are easy to collect, and that they appear to be estrogen responsive. In urine samples collected over the first year, isoflavone concentrations ar 3-5 orders of magnitude higher in children fed soy formula. Equol is not present. We have also collected samples at this site for analysis of a variety of hormones but are still developing methods. We are analyzing the physical examination, ultrasound, and isoflavone data now, and are beginning to plan the next study.